1. Field of the Invention
The invention relates to an improved method for the preparation of tertiary phosphines by cross-coupling of aryl, alkenyl, cycloalkenyl or aralkyl halides, or aryl, alkenyl, cycloalkenyl or aralkyl sulfonate esters, with chlorophosphines in the presence of a catalyst and a reductant.
2. Related Background Art
Tertiary phosphines, especially triarylphosphines, are well known as ligands for transition metal catalysts. Preparation of tertiary phosphines typically proceeds by one of four methods: reaction of halophosphines with aryl Grignard reagents or organolithium reagents, metalation of diarylphosphines followed by reaction with aryl halides or aryl sulfonate esters, Friedel-Crafts reactions of halophosphines with activated aromatic rings, and cross-coupling of aryl halides or aryl triflates with diarylphosphines.
Reactions of aryl Grignard reagents or organolithium reagents with halophosphines are limited to cases in which there are no functional groups present on the aryl moieties which react with the Grignard reagents, such as halo, alkanoyl, or ester substituents. In addition, this method requires special handling procedures for the moisture-sensitive and relatively unstable Grignard reagents or organolithium reagents.
Preparation of tertiary phosphines by metalation of diarylphosphines also requires handling of Grignard or organolithium reagents, with the accompanying problems mentioned above, as well as special procedures necessitated by the fact that diarylphosphines are light-sensitive and pyrophoric. Another disadvantage of this method is that metalated diarylphosphines are extremely nucleophilic and will react with certain functional groups on the aryl moieties of the starting materials, such as halo and alkoxy substituents.
Friedel-Crafts reactions are disadvantageous because they typically employ extremely acidic catalysts such as aluminum bromide, aluminum chloride, ferric chloride, or sulfuric acid. Such catalysts may be incompatible with a variety of functional groups on the aryl moieties. In addition, these catalysts are corrosive and moisture-sensitive, and thus difficult to handle.
As previously mentioned, cross-coupling of aryl halides or triflates with diarylphosphines to produce triarylphosphines is also known.
Tunney and Stille, Journal of Organic Chemistry, Vol. 52, page 748 (1987), prepared triarylphosphines by carrying out a palladium-catalyzed cross-coupling of aryl halides and either (trimethylsilyl)diphenylphosphine or (trimethylstannyl)diphenylphosphine. The major disadvantage of this method is that (trimethylsilyl)diphenylphosphine and (trimethylstannyl)diphenylphosphine are pyrophoric, and thus require special handling procedures. An additional disadvantage is that these reagents are expensive. A limitation of the method of Tunney and Stille is that the trimethylsilyl-substituted starting material, preferred due to the much greater toxicity of the trimethylstannyl compounds, reacts with hydroxyl, amino, nitro, and aldehyde groups on the aryl moieties, preventing application of the method to preparation of triarylphosphines bearing these functional groups. Another limitation is that only aryl halides are used as starting materials, and not arylsulfonate esters. Yet another limitation is that only triarylphosphines are produced by this method because only aryl halides are used as starting materials. There is no suggestion of using benzyl halides as starting materials to make benzylarylphosphines.
A cross-coupling reaction to prepare triarylphosphines is also described in U.S. Pat. No. 5,399,771, which discloses the use of a nickel-catalyzed cross-coupling reaction of a 1,1'-bi-2-naphthol disulfonate ester with diphenylphosphine to produce 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl. This reference exemplifies only the specific transformation mentioned above, and limits the disulfonate ester starting material to the triflate, mesylate or tosylate; no suggestion is made of the possibility of using a halide starting material. A disadvantage of this method is that one of the starting materials, i.e., diphenylphosphine, is light-sensitive and pyrophoric, thus requiring special handling.
The use of diarylchlorophosphines as reagents in the catalytic preparation of tertiary phosphines is neither suggested nor exemplified by the aforementioned references.
A method for production of tertiary phosphines in which the starting materials are inexpensive and easily handled, and which is adaptable to using either aryl or benzyl starting materials containing either halo or sulfonate ester substituents, would be highly advantageous.